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Choosing the Best Bottom Substrate for Your Garden Pond

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The substrate material lining the bottom of your garden pond plays an important role in maintaining water quality and ecosystem balance. Selecting the right type of bottom cover will help create a healthy environment for fish, plants, and other aquatic life. There are several options to consider when deciding what to place on the bottom of a garden pond.

Bare Pond Bottom

A bare pond bottom has no substrate covering the liner or concrete base. This option is easy to clean with a pond vacuum, allowing you to remove debris and prevent accumulation of organic waste However, a bare bottom provides no surfaces for beneficial bacteria to colonize These bacteria help break down fish waste and other nutrients. A bare liner also offers no protection from UV rays which can degrade the liner over time.

Sand

Fine sand provides a natural look and feels pleasant underfoot for wading ponds. Sand easily shifts and settles requiring occasional raking to prevent heavy buildup or compaction in some areas. Sand particles can clog pumps and filters. Sand offers minimal spaces for helpful bacteria to grow. Unless a special coating is applied, plain sand provides little UV protection for the liner.

Pea Gravel

Smooth pea gravel around 1/4-1/2 inch in diameter makes an attractive pond bottom cover. The small stones don’t obstruct water flow or big frequency to colonize. Yet large enough not to enter pumps or clog filters. Pea gravel settles relatively little and is easy to vacuum. Use multiple pounds per square foot to provide a stable base and adequate bacterial habitat.

Small River Rock

For a natural stone appearance, small rounded river rocks 1-2 inches across create an aesthetically pleasing pond bottom. Gaps between the stones allow water flow and debris to settle between rocks. Vacuuming takes more effort, needing to stir up debris. Use a thicker layer of at least 2-3 inches for stability. Smaller rocks will get drawn into pumps.

Large River Rocks

Bigger river rocks over 2 inches across provide large crevices for healthy bacterial populations. The heavier rocks stay put better than smaller gravel. Vacuuming around large rocks is difficult. A thick 3-4 inch minimum layer prevents compaction. Use very rounded rocks to avoid liner damage. Keep rocks away from pump intakes which can jam.

Blended River Rock

A mix of small and large river rocks combines the benefits of the different sizes. The small rocks fill the gaps between larger stones to inhibit debris accumulation while allowing water flow. A 3-4 inch blended mix prevents settling while providing bountiful surfaces for essential nitrifying bacteria. Vacuuming takes more work around the larger rocks.

Cobblestones

Flattened cobblestones offer a visually interesting and textured alternative to rounded river rocks. Their smooth faces won’t damage the liner. Use at least a 2 inch layer to avoid settling. Pond vacuums can remove debris between the gaps. Keep away from pump intakes which could clog. Add larger rocks on top to vary heights.

Crushed Quartz

Crushed quartz like Crystal Quarts provides a shimmering pond bottom that reflects light. The smooth grains won’t harm liners. Silica improves water clarity by absorbing phosphates and organic molecules. Vacuuming quartz is easy with no small particles to clog pumps. Needs at least a 2 inch layer to avoid compaction.

Bentonite Clay

Bentonite clay contains montmorillonite which absorbs nutrients, chemicals, and waste from the water. It provides a natural liner sealant. Bentonite has a high cation exchange capacity to attract and hold positively charged ions. This helps remove ammonia, heavy metals, and other contaminants from ponds.

Pond Soil/Potting Mix

Some ponds use soil, potting mix, or compost on the bottom to create a more natural environment. However, this allows heavy accumulation of organic debris, creating thick sediments lacking oxygen. Anaerobic bacteria generate toxic hydrogen sulfide gas which can harm fish. Must be vigorously stirred often to prevent this.

Best Options for Garden Ponds

For most backyard garden ponds, a 2-3 inch layer of smooth pea gravel, small river rock, or a blend provides the best combination of aesthetics, ease of cleaning, bacterial habitat, and water filtration. Avoid sand and materials with fine particles. Limit soil and organic matter. Add some larger accent rocks. Test pH balance of stone types. Keep intake areas clear. Proper substrate selection creates a healthy garden pond.

What do you put in the bottom of a garden pond?

How to Build a Garden Pond (w/ Monica from The Weekender)

FAQ

Should you put anything in the bottom of a pond?

Rock Bottom Pond Rocks used in ponds provide the following benefits: Adding rocks allows the aerobic bacteria (beneficial bacteria) in your pond a place to colonize and start filtering out debris like fish waste and plant debris. Aerobic bacteria need the presence of ammonia and oxygen in your pond.

What is the best bottom for a pond?

Rocky Pond Bottom Providing varying bottom substrate can allow for more production of forage for your fish. Rocky pond bottom areas are great for crayfish, hellgrammites, and other insect larvae. These are all prime food sources for many fish species, especially Smallmouth Bass.

Should you put rocks in the bottom of a pond?

Pros of having rocks and gravel on pond bottom: Makes the bottom of the pond look natural and hides the liner material. Creates biological environment for beneficial bacteria to break down organic sludge. Rocks and gravel provide media for aquatic plants to attach their roots.

How do you fill a pond with water?

Run the electrical cord up the side of the pond. Plug it into a GFCI outlet. With a good garden hose, fill the pond with water. Stop filling at two to three inches from the rim of the pond. Cover as much pond liner as possible with stonework or aquatic plants since UV rays break down liner materials.

How to build a pond?

Digging the hole is just one step for building a pond. Once you have dug the hole, you will have to smooth it out and then lay pond liner on it. The liner is important because it prevents the water from escaping through. Once you are done, you also need to think about putting something at the bottom of the pond.

Should you put gravel on a pond?

Large ponds generally have mud at the bottom, and that mud usually has a depth of several inches. By adding gravel on top, you are effectively limiting the microbial growth. The gravel also begins to mix in the substrate, which effectively reverses the benefits. If you have a smaller pond, it’s much easier to manage.

How do you protect a pond lining?

If you have built a garden around the pond, it won’t take long before the soil becomes waterlogged due to water leaking from the pond, and many of your plants will die. To protect the lining underneath, you will have to add sand or another material. This will also ensure that the pond liner remains trapped in the bottom.

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